New Method for Measuring the Rates of Ionic Transport and Loss. I. Mobility of NO+

N${\mathrm{O}}^{+}$ ions are produced between parallel electrodes by photoionization, using the Kr resonance line at 1236 Å. Rectangular voltage pulses, separated by a variable time interval, are applied to the electrodes. The transient current, as charges are swept out of the collection region, is displayed on an oscilloscope and recorded photographically; from this curve the mobility of the charge carriers may be deduced. Experimental values for the mobility of N${\mathrm{O}}^{+}$ in He, Ar, ${\mathrm{N}}_2$, and ${\mathrm{H}}_2$ at 20°C and 760 mm Hg are: 19.1±2.4, 3.7±0.2, 3.3±0.2, and 16.3±1.2 ${\mathrm{cm}}^2$ ${\sec }^{-1\mathrm{}}$ ${\mathrm{V}}^{-1\mathrm{}}$, respectively. The mobility of N${\mathrm{O}}^{+}$ in He-${\mathrm{N}}_2$ mixtures obeys Blanc's law, thus indicating negligible complexing of N${\mathrm{O}}^{+}$ with ${\mathrm{N}}_2$ or He. The integrated transient current is related to the total charge in the collection region at the initiation of collection; the rate of growth of ion density as the time interval between pulses is increased indicates the predominant ion loss process and its rate. In these experiments, the integrated current is consistent with ion loss by diffusion, with $D=\frac{\mathrm{KkT}}{e}$, where $K$ is the experimental ion mobility. The transient current shape, the role of space charge, and the initial charge distribution have been treated theoretically.